Pospisil, Sock in fine form

Reigning Wimbledon men's doubles champions Vasek Pospisil and Jack Sock made their mark in the singles event at the BB&T Atlanta Open as they each qualified for the quarter-finals.

Canada's Pospisil and Sock of the United States caused one of the biggest shocks at the All England Club this year by beating top seeds Bob and Mike Bryan in the final, and they have both been in form this week.

Fourth seed Pospisil eased past Ukraine's Illya Marchenko 7-5 6-3, while Sock was a 6-4 6-2 winner over New Zealand qualifier Michael Venus.

"It wasn't easy. It was very hot and humid," Pospisil said. "It was difficult to find a balance between saving my energy and being focused. I think I balanced both really well. I won the big points. That was key."

Seventh seed Yen-Hsun Lu defeated Alex Kuznetsov 6-4 6-4, but Denis Istomin, seeded sixth, was sent packing as Lukas Lacko hit back from a set down to claim a 5-7 6-1 6-4 victory.

Sam Querrey also crashed out after a 6-2 6-4 loss to Israel's Dudi Sela despite the ninth seed winning 86 per cent of points on his first serve.